Excitation system for a synchronous machine

ABSTRACT

The present invention relates to an excitation system for a synchronous machine. The system according to the invention is characterized in that at least one phase of an additional winding has at least one of the coils with a reduced number of turns as compared with the number of turns in the remaining coils of that phase, and the number of turns in that coils can be reduced to zero.

United States Patent Arutjunian et al.

EXCITATION SYSTEM FOR A SYNCHRONOUS MACHINE Inventors: Vladimir Semenovich Arutjunian, ulitsa Marxa, 8, kv. [8; Sergei Grigorievich Amamchian, ulitsa Ta- 1 Jan. 30, 1973 [56] References Cited UNITED STATES PATENTS 3,025,450 311962 Krabbe 322/79 X 3,035,222

5/1962 Stone ..322/59 X Primary Examiner-J. D. Miller Assislan! ExaminerH. Huberfeld Atl0rney-Erich H. Waters et al.

57 ABSTRACT The present invention relates to an excitation system for a synchronous machine.

The system according to the invention is characterized in that at least one phase of an additional winding has at least one of the coils with a reduced number of turns as compared with the number of turns in the remaining coils of that phase, and the number of turns in that coils can be reduced to zero. t

4 Claims, 11 Drawing Figures PATENTEUJAN 30 1915 SHEET 1 UF 3 PATENTEDJAN 30 I975 3.714.542

SHEET 3 or 3 5 z H a 7 F169 EXCITATION SYSTEM FOR A SYNCIIRONOUS MACHINE The present invention relates to electric machines, and more specifically to an excitation system for a synchronous machine, utilizing energy at the third and higher harmonics of the air-gap field.

Known in the prior art is an excitation system for a synchronous machine, comprising an armature winding located jointly with a multi-phase additional winding each phase of which is made up of separate coils and which is wound for three times as many poles as the armature winding, and also a field winding energized from said additional winding via a rectifier (see, for example, US. Pat. No. 3,025,450, 1959).

This prior-art excitation system utilizes the third and higher harmonics of the magnetic field established in the air gap. As will be recalled, the performance of the machine itself and of its excitation system can be improved by the utilizing, in addition to the energy due to higher field harmonics, also energy of the fundamental air-gap field. This additional utilization of the energy due to the field at the fundamental frequency improves the performance of the machine owing to the greater ease with which the desired variations in the energy of the excitation system can be obtained according to the magnitude of the load; the improved performance of the excitation system at low and no-load despite the spread in the size and shape of the air-gap occurring in manufacture and operation; and improved initial selfexcitation.

In the case of a partial utilization of energy supplied by the fundamental field, it is preferable to make one phase of the additional winding which energizes the field winding via rectifiers in such a manner that the resultant field induces in this phase not only the emfs at the triplen and higher frequencies, but also a fraction of the emfdue to the fundamental frequency.

For this purpose, in a conventionally made additional winding the phase in which no emf at the fundamental frequency is to be induced in addition to the emfs at the triplen and higher harmonics has some of its turns or coils removed from the electric circuit.

This upsets the compensation of the fundamental emf in the various parts of the phase, and an emf at this frequency appears.

Since the relative content of the fundamental frequency in the resultant air-gap field is much greater than that of the higher harmonics, it is necessary to remove only a small part of that phase in the additional winding in order to secure the desired magnitude of the emfat the fundamental frequency.

For this reason, there is no marked decrease in the energy due to the third and higher field harmonics, so essential to the self-control of excitation.

This prior-art configuration of a phase in the additional winding suffers from the following disadvantages.

To begin with, removal of even a small part of the phase from the circuit impairs the utilization factor of the machine. Furthermore, from considerations of manufacturing, the part of the winding electrically removed from the circuit should in some cases be preferably left in the slots in order to fill them all to the same extent, and this involves increased consumption ofmaterials.

It is an object of the present invention to avoid the above-mentioned disadvantages.

The invention aims at providing an excitation system for a synchronous machine, utilizing the higher harmonics and fundamental frequency of the field and has a simpler construction and better electrical performance.

With these objects and aims in view, the invention resides in that in at least one phase of the additional winding at least one of its coils has a reduced number of turns as compared with the number of turns of the remaining coils of that phase, so that the number of turns in that coil can be reduced to zero.

It is preferable that the armature of the machine should carry a second additional win ding made up of coils filling up the phase belts of the first additional winding and connected on the d.c. side via a rectifier to the field winding or directly in opposition to the first additional winding.

It is also preferable that the second additionaly winding be connected into an open delta and coupled to the first additional winding.

An excitation system made substantially as described herein successfully achieves the sought objectives.

The invention will be more fully understood from the following description of preferred embodiments when read in connection with the accompanying drawings,

wherein:

FIG. 1 is a schematic diagram of an excitation system for a synchronous machine, utilizing the third and higher harmonics owing to provision of an additional winding with a reduced number of turns;

FIG. 2a and b shows a schematic diagram of one phase of the additional winding, formed by connecting into an open delta three identical sections spaced electrical degrees apart, with one of the coils in the additional winding having a reduced number of turns; and also the waveforms of the emfs due to the fundamental frequency and 3rd harmonic;

FIG. 3 shows a schematic diagram ofthe additionalwinding phase with a reduced number of turns, wound from identical coils for three times as many poles as the main armature winding, and also the waveforms of the emfs due to the fundamental frequency and 3rd harmonic;

FIGS. 4 and 5a and b shown the vector diagram of the arrangement of FIG. 1 for the emfs due to the fundamental frequency and the 3rd harmonic, respective 3 FIGS. 6 and 7a and b show the vector diagrams of the arrangement of FIG. 2, for the emfs due to the fundamental frequency and the 3rd harmonic of the field, respectively;

FIG. 8 is a schematic diagram of an excitation system for a synchronous machine with a second additional winding connected on the d.c. side in parallel with the first additional winding;

FIG. 9 shows the same as FIG. 8, but with the windings connected in series;

FIG. 10 is a schematic diagram of an excitation system for the same machine, with a second additional winding made up of coils filling up the phase belts of the first additional winding and connected in opposition with the latter;

FIG. 11 shows an embodiment of the arrangement of FIG. 10, in which the second additional winding is connected in an open delta.

Referring to FIG. 1, there is an excitation system for a synchronous machine, comprising a main armature winding 1 jointly located with a multi-phase additional winding 2 which energizes a field winding 4 via a rectifier 3.

In each phase of the additional winding 2 wound for three times as many poles as the main armature winding 1, emfs are induced at the 3rd and higher harmonics of the field frequency. Besides, in order to supply the lacking excitation energy (at no-load or low load), the field energy due to the fundamental frequency is added to the field set up by the additional winding, by removal of a part 5 of its turns or coils from the phase circuit of the winding (in FIG. 1, this part 5 of the winding is shown by the dotted line).

Each phase of the additional winding 2 can be formed either by three identical sections a, b, and connected in an open delta and spaced I20 electrical degrees in the main field and wound similarly to the main armature winding 1 but with a pitch very close to the diameter pitch (FIG. 2a), or by coils with a pitch close to one-third of the diameter pitch and wound for three times as many poles as the main winding (FIG. 3a). The phase sections of the winding are connected so that the section of the winding 2 shown by the dotted line (FIG. 2a) is removed from the electric circuit. The removed turns account for an insignificant proportion of the total volume of the additional winding 2, being only a few per cent, so that the relative content of the fundamental frequency in the resultant field is much greater than that of the higher harmonics.

In a conventional winding, the vector sum of the emfs due to the fundamental field is zero, so that removal of even a small number of turns from the circuit results in a marked emf due to the fundamental frequency (FIGS. 4 and 7), which, with a properly adjusted number of removed turns, has the desired effect on the excitation energy, especially at low load.

In this case, the induced emfdue to the fundamental frequency (FIGS. 2a and 3a) is represented by the vector from H1 to K1 in the vector diagram of FIGS. 4a and 7a. At the same time, the emf due to the 3rd harmonic of the field decreases, even though by a small amount. The emf due to the 3rd harmonic is represented by the vectors from H3 to K3 in the vector diagrams of FIGS. 4b and 7b.

Present in each phase of the additional windings are the emfs due to the fundamental frequency, 2 (FIG. 1), and due to the 3rd harmonic, e The emfinduced in the part of the phase, electrically removed from the circuit but bodily left in the slots of the machine, is e, equal in magnitude but opposite in sign to e induced'in the remainder of the winding 2 furnishing the greater proportion of the excitation current, and also the triplen-harmonic emfe which is in the same direction as e in the other phase. The desired ratio between e and e;, can be ensured by positioning the neutral point appropriately.

In order to improve the utilization of the additional winding 2 and of the space on the armature intended for its location, the part 5 of the additional winding 2, instead of being removed from the electric circuit, may

by utilized for, rather than eliminated from, the process of excitation. For this purpose, the removable part5 of the additional winding 2 may be connected to the field winding via a rectifier in parallel (FIG. or in series (FIG. with another, previously utilized part of the additional winding 2. As a result, the energy entering the field winding 4 will increase. At the same time, the fundamental-frequency component of the field will account for a greater share of the total field. The additional windings 2 and 5 (FIGS. 8 and 9) placed together with the main armature winding 1 in the slots of the armature have no direct electrical connections with one another.

However, parts of the additional windings 2 and 5 may be interconnected and arranged in any one of several methods (FIGS. 10 and 11), in order to obtain the desired energy due to the fundamental frequency of the field.

In FIG. 10, part 5 of one phase in the additiona winding 2 is connected in opposition to the greater part of the phase in that winding, with the result that the emfs due to the fundamental frequency of the field in both parts are added together: e e 2e while the emfs due to the 3rd harmonic are subtracted: e 2

FIG. 11 shows the parts of the additional windings 2 and 5 connected so that the energy due to the fundamental frequency of the field with the same number of turns in parts of the additional windings 2 and 5 as in the arrangement of FIG. 10 differs from the energy in the latter arrangement, while the emf due to the 3rd harmonic in part 5 of the winding connected into an open delta is balanced out and cannot be subtracted from the emf due to the fundamental frequency in the additional winding 2.

Thus, a second additional winding made up of coils filling up the phase belts in the first additional winding ensures the desired ratio of the emfs due to different frequencies controlling the self-regulation of excitation and improves the electric performance of the excitation system built in this case into the machine itself.

What is claimed is:

1. An excitation system for a synchronous machine,

comprising: a main armature winding located jointly with a multi-phase additional winding each phase .of which is made up of coils and which is wound for three times as many poles as said armature winding; a field winding energized from said additional winding via a rectifier; at least one phase ofthe additional winding having at least one coil with a reduced number of turns as compared with the number of turns in the remaining coils of the same phase, and the number of turns in that coil can be reduced to zero.

2. An excitation system, as in claim 1, in which the armature carries a second additional winding made up of coils filling up the phase belts of said first additional winding, and connected on the dc. side via a second rectifier to said field winding.

3. An excitation system, as in claim 1, in which the armature carries a second additional winding made up of coils filling up the phase belts of the said first additional winding and connected in opposition to the latter.

4. An excitation system, as in claim 1, in which the armature carries a second additional winding connected in an open delta and coupled to said first additional winding. 

1. An excitation system for a synchronous machine, comprising: a main armature winding located jointly with a multi-phase additional winding each phase of which is made up of coils and which is wound for three times as many poles as said armature winding; a field winding energized from said additional winding via a rectifier; at least one phase of the additional winding having at least one coil with a reduced number of turns as compared with the number of turns in the remaining coils of the same phase, and the number of turns in that coil can be reduced to zero.
 1. An excitation system for a synchronous machine, comprising: a main armature winding located jointly with a multi-phase additional winding each phase of which is made up of coils and which is wound for three times as many poles as said armature winding; a field winding energized from said additional winding via a rectifier; at least one phase of the additional winding having at least one coil with a reduced number of turns as compared with the number of turns in the remaining coils of the same phase, and the number of turns in that coil can be reduced to zero.
 2. An excitation system, as in claim 1, in which the armature carries a second additional winding made up of coils filling up the phase belts of said first additional winding, and connected on the d.c. side via a second rectifier to said field winding.
 3. An excitation system, as in claim 1, in which the armature carries a second additional winding made up of coils filling up the phase belts of the said first additional winding and connected in opposition to the latter. 